Display screen or portion thereof including a graphical user interface



The FIGURE is a front view of a display screen or portion thereof including a graphical user interface showing our new design.

The broken line showing of a display screen or portion thereof including a graphical user interface is included for the purpose of illustrating portions of the article and forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof including a graphical user interface, as shown and described. 